Tape drive having a selectively retractable drive hub

ABSTRACT

In order to enable a tape drive machine to be constructed in a housing (30) with low height, a hub (36) which in operation projects from a drive motor (34) into a tape cartridge (10) is retractable into the motor (34) to permit the cartridge (10) to be slid out from the machine in the edgewise direction. In an alternative embodiment, the motor and hub can be slid part-way out of the housing (30). A tape drive machine also discloses indexing of a tape drive head, a path for the tape, threading of the tape, the drive motor, construction of a motor stator, and detection of the beginning and end of tape.

1. INTRODUCTION

This invention relates to tape drive machines for magnetic or opticaltape, or other types of data storage tape. Various aspects of theinvention are concerned with loading a cartridge into a tape drivemachine, a hub of a tape drive motor, indexing of a tape drive head, animproved tape path through a tape drive machine, threading of the tapeinto the tape drive machine, a tape drive motor, a construction of motorstator and a dual performance motor. In this specification, the tapedrive apparatus is described in one particular orientation, but theclaims should be interpreted to cover the apparatus whether in thatorientation or bodily turned, for example, through a right angle.

1.1 Cartridge Loading

This aspect of the invention is particularly concerned with a tape drivefor use with a single reel 5"×4"×1" (127 mm×102 mm×25 mm) (nominalsizes) tape cartridge according to, for example, specification IBM GS32-0048-0, ECMA 120 or ANSI X3B5-87-037. An example of such a product isthe IBM 3480 cartridge. Such a cartridge is shown schematically in FIGS.1A to 1C. The cartridge has a generally flat rectangular housing 10 withupper and lower faces 12, 14 and a peripheral wall 16. At one corner 16of the housing, a leader block 18 is a snap-fit in the housing, and, inuse, the block 18, to which one end of the tape is attached, isunclipped from the housing and is used to withdraw the end of the tapeand thread the tape through the tape drive machine and onto a take-upreel. The lower face 14 of the housing has a circular aperture 20 whichprovides access to a supply reel drive member 22 having a ring of teeth24. A locking button 26 is formed at the center of the drive member 22.In use, a supply reel hub of the tape drive machine depresses the drivemember 22 upwardly into the housing by about 4 mm, and dogs on thesupply reel hub engage the teeth 24. Furthermore, a release member onthe supply reel hub engages the locking button 26 and depresses it afurther 2 mm or so. The supply reel can then rotate in housing 10 and bedriven by the supply reel hub through the action of the interengagingdogs and teeth 24.

It is known to provide the tape drive machine in what is termed a 51/4"profile industry standard enclosure, which is so called because it wasthe size of the enclosure for the initial 51/4" floppy disc drives. Suchan enclosure measures 8"×5.75"×3.25" (203 mm×146 mm×83 mm) excluding anyfascia. A typical method of loading a 5"×4"×1" tape cartridge into suchan enclosure is illustrated in FIG. 2. In that drawing, referencenumeral 30 denotes the enclosure, which has an aperture 32 in the frontpanel to receive the cartridge 10 edgeways. A supply reel motor 34 witha drive hub 36 is mounted in the enclosure 30. As the cartridge is slidin edgeways, it is guided for movement along the path indicated by thechain dot lines from position 10(1), through position 10(2) to operatingposition 10(3), as shown in dashed lines. It will be noted that thecartridge drops downwardly onto the supply reel hub 36 between position10(2) and 10(3), and this movement is essential to enable the hub 36 totake up engagement with the drive member in the cartridge.

One design desideratum is to make computer equipment as small aspossible, but a restraint on this is the need to fit in with existingindustry standards. Developments in the design of floppy disc driveshave now enabled a drive to be manufactured in an enclosure which ishalf of the height of the original industry standard. This is termed ahalf-height 51/4" profile enclosure and thus enables two floppy discdrives to be stacked in the space of a previous full-height 51/4"profile enclosure. The nominal dimensions of the half-height 51/4"profile are 8"×5.75"×1.625" (203 mm×146 mm×41 mm).

Consideration has been given to shrinking the size of a 5×4×1 cartridgedrive so that it fits into the half-height 51/4" profile, but withoutany success. Indeed, referring to an article in "Systems International"December 1984 relating to developments in the tape drive industry, it issaid on page 48:

"How small a package will the IBM cartridge fit into?. . . A 5×4×1 . . .will easily fit into a standard 8 in footprint with desirableperformance parameters, but it will certainly not fit into a half-high51/4 in footprint with present technology feasabilities. Whether it willfit into a full-high 51/4 footprint will be decided by the ingenuity ofthe OEM drive manufacturers".

One of the most significant problems with fitting a 5"×4"×1" drive intoa half-height 51/4" profile is the height limitation. The height of theprofile is 41.3 mm. With 1 mm thick top and bottom housing plates, theinterior height is 39.3 mm. The cartridge height is 25.2 mm, whichleaves 14.1 mm spare to accommodate the height of the supply reel motorand the hub, and to provide necessary clearances. The hub and releasebutton have to protrude about 8 mm above the motor, and with 1 mm beingleft for clearance, this enables a motor of only 5.1 mm in height to beused. With present technology, it has not been possible to construct amotor of this height with the required drive characteristics.

The first aspect of the invention is concerned with providing solutionsto problem set out above.

One solution to the problem in accordance with the invention is providedby a tape drive comprising a housing defining a space to receive acartridge in an operating position, a motor having a body disposed inthe drive housing directly below the bottom wall of a cartridge disposedin the operating position, a drive hub projecting from the motor intothe cartridge receiving space to engage and drive the hub receivingmember of a cartridge disposed in the operating position, and means toretract the drive hub into the motor to permit a cartridge to bewithdrawn from the operating position substantially by sliding movementonly in an edgewise direction of the cartridge.

Another solution to the problem in accordance with the invention isprovided by a tape drive comprising a housing defining a space toreceive a cartridge in an operating position, a motor having a bodydisposed in the drive housing directly below the bottom wall of acartridge disposed in the operating position, a drive hub projectingfrom the motor into the cartridge receiving space to engage and drivethe hub receiving member of a cartridge disposed in the operatingposition and means to guide the motor, drive hub and a cartridgedisposed in the operating position substantially for sliding movementonly in an edgewise direction of the cartridge to permit the cartridgeto be withdrawn from the operating position to a position in which themajority of the cartridge is outside of the housing.

Both of the solutions, therefore, provide a tape drive which includes ameans to permit a cartridge to be withdrawn from the operating positionto a position in which at least the majority of the cartridge is outsideof the housing substantially by sliding movement only in an edgewisedirection of the cartridge.

1.2 Drive Hub

For use with the arrangement employing a retractable drive hub, thepresent invention provides, according to a further aspect thereof, adrive mechanism comprising a motor having an annular rotor, a tape reeldrive hub mounted within the rotor, means to cause the hub to move inopposite axial directions between first and second axial positions withrespect to the rotor upon relative rotation of the hub and rotor infirst and second opposite directions, and means selectable to lock thehub in at least the first of said axial positions so that rotary drivecan be transferred from the rotor to the hub.

The means to cause the hub to move axially preferably comprises a screwthread or the like acting between the hub and the rotor. In one example,at least one projection may be provided on one of the rotor and the hubengaging in a complementary groove in the other or the rotor and thehub. In another example, both the rotor and the hub are formed withgrooves, with balls being provided to run in the associated grooves toprovide a screw-drive action.

The mechanism is preferably arranged so that the hub is prevented frommoving from the second axial position past the first axial position withrespect to the rotor, the locking means comprising a brake operable toprevent relative rotation between the hub and the rotor in the directionwhich will cause the hub to move from the first to the second axialposition with respect to the rotor.

1.3 Head Indexing

It is common to record data on a magnetic tape in a plurality of tracksspaced apart across the width of the tape. In order to write to or readfrom the plurality of tracks, either a multi-track head may be used, oralternatively a single track head may indexed across the width of thetape to the appropriate position. The drive to move the head may beprovided by a stepper motor, or a DC motor and encoder, and anappropriate gear mechanism. It is also common to provide for azimuthadjustment of the head. In a basic arrangement, a manual azimuthadjustment is provided, and the azimuth angle of the head is set whenthe machine is built, and can be adjusted when the machine is serviced.

This aspect of the invention is concerned with enabling a more compactarrangement to be provided to serve the purpose of indexing the headacross the tape and also adjusting the azimuth angle of the head. Inaccordance with this aspect of the invention, there is provided a datahead indexing system comprising a reversible motor, and first and secondmechanisms driven by the motor for indexing first and second portions,respectively, of the head in opposite directions across a recordingmedium, the first mechanism incorporating a backlash device so that, asthe mechanisms drive the head in unison, the head is bodily moved acrossthe recording medium, but so that, as the backlash of the backlashdevice is being taken up, the second mechanism alone moves the firstportion of the head to adjust the azimuth angle of the head relative tothe recording medium. Thus, the system provides for indexing and azimuthadjustment with the use of only a single motor.

The system preferably also includes means for controlling the motor, thecontrol means being operable when moving the head in one direction tocause the motor to drive the second mechanism in one direction and takeup the backlash in the first mechanism and then to drive the first andsecond mechanisms in unison in said one direction to move the head insaid one direction, and then to drive the second mechanism in theopposite direction while there is backlash in the first mechanism toachieve a desired azimuth angle of the head. Conversely, the controlmeans is preferably operable when moving head in the opposite directionto cause the motor to drive the second mechanism in the oppositedirection and take up backlash in the first mechanism and then to drivethe first and second mechanisms in unison in said opposite direction tomove the head in said opposite direction, and then to drive the secondmechanism in said one direction whilst there is backlash in the firstmechanism to achieve a desired azimuth angle of the head.

1.4 Tape Drive Motor

This aspect of the invention is concerned with providing a motor ofsmall axial length, thus making the motor particularly suitable forfitting into a half-height 5 1/4" profile between the tape cartridge andthe bottom plate of the enclosure.

Typically, the rotor of an electric motor is mounted in the motorhousing by two bearings, and for precision motors, it is also necessaryto provide some means, such as a spring or shims, to take up any endplay in the rotor.

In order to enable the axial length of the motor to be shortened, thisaspect of the invention provides an electric motor comprising a statorand a rotor, the rotor being mounted to the stator by a single bearingassembly, and the arrangement being such that, in operation, themagnetic field acting between the stator and the rotor has a substantialcomponent in the axial direction of the rotor, so that the rotor exertsan axial force on the bearing.

Preferably, the bearing is a ball bearing assembly. Any play between theballs and the raceways of the bearing assembly, which would otherwiseallow axial movement and tilting of the rotor relative to the strator,is taken up when the motor is operational by the axial component of themagnetic field.

Preferably, the diameter of the bearing assembly is a substantialproportion such as at least a quarter, and more preferably about onehalf, of the overall diametrical size of the motor, in order to reducethe possible tilting of rotor. The balls of the bearing are preferablyof small diameter relative to the diameter of the path they follow, forexample in the ratio of 1:10, or less.

1.5 Stator Construction

This aspect of the invention is concerned with constructing a statorwinding assembly for use in a flat profile motor. The method comprisesthe steps of arranging a plurality of winding coils in a first ring as afirst tier, arranging a further plurality of winding coils in a secondring as a second tier on the first tier so that the windings of thesecond tier are angularly off-set relative to the windings of the firsttier. This aspect of the invention is characterised in that the twotiers are pressed together to deform the windings so that portions ofthe windings of each tier are interleaved with portions of the windingsof the other tier. The windings are then secured together.

This construction method provides a compact and strong stator assembly.

The stator may be constructed from more than two tiers following theprinciples described above.

Preferably, the winding coils are coated with a heat-curable materialprior to arranging the coils in the tiers, and after pressing the coilstogether the assembly is heated in order to cure the material and thusbond the winding coils together. A dough moulding compound (DMC) orother form of encapsulation ensures a rigid structure.

1.6 Tape Edge Detection

It is known in a tape drive machine to attempt to ensure that theposition of the head transversely across the tape is accurately set byguiding one edge of the tape with respect to a reference surface such asa fixed flange on a roller which also has a light spring-loaded flangeso that the opposite edges of the tape are squeezed between the flanges.The position of the head is set with respect to the reference flange ora further reference surface fixed with respect to the reference flange.A problem with this known arrangement is that errors can still arise,for example, due to the tape not being fed in a direction perpendicularto the axis of the roller. Also the spring loaded flange of thereference roller tends to damage or increase wear of the tape.

In accordance with this aspect of the invention there is provided a tapedrive machine comprising a head, means to drive a tape from one reel toanother past the head, means to detect the position of an edge of thetape in a direction transverse to the tape at a location adjacent thehead and means to adjust the transverse position of the head and thetape relative to each other in dependence upon the sensed edge position.

In a preferred embodiment, the detecting means comprises means toproject a beam of light across the edge of the tape, and a light sensorarranged to sense the beam and such that the tape casts a shadow on thesensor, the sensor producing an output signal dependent upon theposition of the shadow on the sensor. Preferably the distance betweenthe tape and the sensor is substantially greater than that between thesource and the tape, so that movement of tape in the transversedirection is amplified as movement of the shadow. For furthersensitivity, the beam preferably has a small dimension in the directiontransverse to the tape at the source of the beam and diverges from thesource. Conveniently, the source of the beam may be a laser diode. Thesensor may include means to compensate for variations in the intensityof the beam.

1.7 Beginning and/or End of Tape Detection

It is necessary in a tape machine to be able to detect when thebeginning of the tape is approaching on reverse wind, or the end of thetape is approaching on forward wind. In one known method, the stationsof the supply and/or take-up reel are counted up and down, and nearingof the beginning or end of the tape can then be determined. This methodhas the drawback, however, that in the case of power loss, the countwill also be lost unless a non-volatile memory is employed. If the countis lost, then the machine must be operated at very low speed to returnto the beginning of the tape where some other means may be utilised todetect the very beginning of the tape, such as data written on the tape,a sensor which detects a reflective end portion of the tape, or theleader block being pulled out of its recess in the take-up reel.

In accordance with this aspect of the invention, there is provided atape drive machine operable to wind tape between a pair of reels andhaving:

means to provide a signal indicative of the linear speed of the tapebetween the two reels;

means to provide a signal indicative of the angular speed of one of thereels; and

means to determine from the tape speed signal and the reel speed signal,when less than a predetermined amount of tape remains on said one reel.

Because there is a predetermined relation between the angular speed ofthe reel and the linear speed of the tape when the reel is empty (i.e.the linear speed is equal to the reel radius multiplied by the angularspeed), the beginning or end of tape can be detected without needing tocount the reel revolutions.

Preferably, the machine further comprises means to provide a signalindicative of the angular speed of the other reel, and means todetermine, from the tape speed signal and the other reel speed signal,when a predetermined amount of tape remains on said other reel. Thusboth the beginning and end of the tape can be simply detected.

The machine may further comprise means to control rotation of the reelsin dependence upon result of the determination(s) made by thedetermining means. For example, upon a fast rewind operation the reelsmay be reduced to a slow speed when the beginning of the tape isdetected, and upon a fast forward winding operation the reels may bereduced to a slow speed when the end of the tape is detected.

1.8 Last Turn Detection

As mentioned above, it is known to detect when the very beginning of thetape is reached either by marker data written on the tape or a sensorwhich senses a reflective portion at the end of the tape. The markerdata method therefore requires the tape to be read as it is beingrewound. The reflective portion method requires the tape to be speciallymanufactured to include a reflective portion or requires a reflectivelabel to be affixed to the tape.

In accordance with this aspect of the invention, there is provided atape drive machine operable to wind tape between a pair of reels andcomprising means to detect when the tape does not cover part of one ofthe reels. Thus, the only requirement of the tape is that it is notlight transmissive, which is generally the case. When the last turn ofthe reel is reached, the tape uncovers said part of the reel and thedetection is then made.

Preferably, the detecting means comprises means to project a beam oflight along a path which includes a passageway through said part of thereel, and means to determine when the light path is cut by the tape.

The last turn detection may be conveniently used with a means to controlrotation of the reels in dependence upon the detection made by thedetection means.

This aspect of the invention is preferably used in conjunction with thebeginning of tape detection method described above at Section 1.7.

Various combinations of the above described aspects of the inventionmay, of course, be embodied in the same machine.

2. LIST OF DRAWINGS

Specific embodiments of the invention will now be described by way ofexample with reference to the accompanying drawings, in which:

FIGS. 1A, 1B and 1C are plan, side and under plan views, respectively,of a 4"×5"×1" tape cartridge;

FIG. 2 is a schematic side view of a known tape drive mechanism;

FIG. 3 is a schematic side view of a tape drive machine in accordancewith the invention, with a tape cartridge shown in the operativeposition;

FIG. 4 is a view similar to FIG. 3, but showing a tape cartridgepartially withdrawn, using one system according to the invention;

FIG. 5 is a view similar to FIG. 3, but showing a tape cartridgepartially withdrawn, using another system according to the invention;

FIG. 6 is a partially cut-away perspective view, partly from below, of adrive hub retracting mechanism;

FIGS. 7A, 7B and 7C illustrate the operation of the drive hub mechanism;

FIGS. 8A and 8B are side views illustrating the drive mechanism;

FIG. 9 is a schematic illustration of a recording head indexingmechanism;

FIGS. 10A to 10E illustrate the operation of the recording head;

FIG. 11 is a sectional view through a motor;

FIG. 12 is a plan view of the winding arrangement of the motor;

FIG. 13 is a side view of the winding arrangements;

FIGS. 14 and 15 are sectional views of the winding arrangement takenalong the section lines 14--14 and 15--15, respectively, as shown inFIG. 12.

FIG. 16 is a block diagram illustrating the manner of control of themotor;

FIG. 17 is a schematic diagram illustrating a tape sensing arrangement;

FIG. 18 shows a photo-sensor array used in the arrangement of FIG. 17;

FIG. 19 shows an alternative photo-sensor; and

FIG. 20 is a sectioned elevation of a take-up reel showing an last turnsensor.

3. DESCRIPTION OF THE EMBODIMENTS 3.1 Cartridge Loading

Referring to FIG. 3, the enclosure of a tape drive machine according tothe invention has a nominal height of 41 mm. A low height motor 34 ismounted adjacent the floor of the housing 30, and a drive hub 36projects upwardly from the motor 34 into engagement with the drivereceiving member 22 of a standard cartridge disposed in an operatingposition, as shown in dashed lines in FIG. 3, in the enclosure 30.

Referring to FIG. 4, in accordance with one embodiment of the invention,the drive hub 36 can be retracted into the height of the motor 34, andthus the tape cartridge 10 can be withdrawn from the enclosure 30 solelyby movement in the edgeways direction, as denoted by arrow 38, and adifferent cartridge can then be loaded into the enclosure 30, whereuponthe drive hub 36 is raised into engagement with the replacementcartridge.

Referring to FIG. 5, in an alternative embodiment, the hub 36 is notretractable, but instead the motor 34, together with the hub 36 ismounted for sliding movement in the edgewise direction of the cartridge10, as denoted by the arrow 40, to a position in which all or nearly allof the cartridge is disposed outside of the enclosure 30, whereupon thecartridge 10 can be lifted clear of the drive hub 36 and completelyremoved from the drive machine. A replacement cartridge can then bedropped onto the drive hub, and the motor 34, drive hub 36 andreplacement cartridge 10 can then be slid into the machine in thedirection opposite to arrow 40 to the position as shown in FIG. 3.

3.2 Drive Hub

Referring to FIG. 6, the retracting hub mechanism described withreference to FIGS. 3 and 4 is illustrated. The motor 34 has an annularrotor 42 with a cylindrical wall 44. The drive hub 36 is generallycylindrical and is fitted within the cylindrical wall 44 of the rotor.The outer cylindrical surface of the drive hub 36 is formed with threesomewhat helical grooves 46, and corresponding pins 48 project from theinner cylindrical surface of the annular rotor 42 into engagement withthe grooves 46 so that relative rotational movement between the drivehub 36 and rotor 42 produces axial movement of the hub relative to therotor. If need be, a further set of pins may be provided at a differentaxial position to the pins 48 so that for one portion of the axialmovement of the hub 36 the pins 48 engage the grooves 46 and so that foranother portion of the movement of the hub the further pins engage thegrooves, there being an overlap when both sets of pins engage thegrooves. In one alternative arrangement, the pins may be provided on thehub 36, rather than on the wall 44, and the grooves may be provided inthe wall 44, rather than in the hub 36. In another alternativearrangement, grooves may be formed in the hub 36 and the wall 44, andballs may be provided between the grooves so that the arrangement actsas a ball screw. Three wedge shaped recesses are formed around the outersurface of the drive hub 36, and each recess 50 is fitted with a wedgeshaped brake element 52. The wedge shapes of the recess 50 and the brakeelement 52 are complementary and produce a jamming action between thebrake element 52 and inner surface of the rotor wall 44, underassistance of a spring 54 when the rotor 42 is driven in one direction.

A tubular internally splined brake release member 56 is fitted insidethe drive hub 36. The brake release member has a radial projection 58engagable in a recess in the internal cylindrical wall of the drive hub36 to limit relative movement of the brake release member relative tothe drive hub. Furthermore, the brake release member has three radiallyoutwardly facing recesses 60, into each of which an operating arm 62projects from a respective one of the brake elements 52. A latching unit66 is mounted relative to the stator of the motor within the splinedinterior of the brake release member 56 and has a latch element 68 whichcan be operated by a ligament 70 against the action of a return spring72 to project into engagement with the splines 74 of the break releasemember 56.

The operation of the drive hub arrangement of FIG. 6 will now bedescribed with reference to FIGS. 7A, 7B and 7C.

Referring to FIG. 7A, and commencing with the arrangement in which thedrive hub 36 is retracted into the rotor 42, in order to make the hubrise, the ligament 70 is tensioned and the rotor 42 is rotated clockwisewhen viewed from the underside of the drive. Tensioning the ligament 70causes the latch element 68 to engage with the splines 74 of the brakerelease member 56 and thus prevents rotation of the brake release member56. The projection 58 prevents the drive hub 36 from rotating. Relativerotation between the rotor 42 and the drive hub 36 is permitted by thebrake elements 52, because the relative rotation is in a direction totend to un-jam the brake elements. The relative rotation between therotor 42 and the drive hub 36 causes the drive hub 36 to rise throughthe action between the pins 48 and the grooves 46 until the pins 48reach the ends 74 of the grooves.

The arrangement then jams until the latch element 68 is disengaged fromthe splines 74 by releasing the tension on the ligament 70. Referring toFIG. 7C, upon such release, the drive hub 36 can be turned in eitherdirection by the rotor 42. Relative rotation between the drive hub 36and rotor 42 is prevented in one direction by engagement of the pins 48with the ends 74 of the grooves 46, and is prevented in other directionby the jamming action of the brake elements 52 against the innercylindrical wall of the rotor 42.

Referring to FIG. 7B, in order to retract the hub 36 into the rotor 42,the rotor is driven in the anti-clockwise direction, when viewed fromthe underside of the drive, and the ligament 70 is tensioned. Upontensioning of the ligament, the latch element 68 is re-engaged with thesplines 74 in the brake release member 56. Thus, the brake releasemember 56 is stalled. The release arms 62 on the brake elements 52 aretherefore engaged by the recesses in the brake release member 56 andcause the brake elements 52 to become un-jammed from the rotor 42. Also,the projection 58 on the brake release member 56 prevents the drive hub36 from rotating, and therefore the relative rotation between the rotor42 and the drive hub 36 causes the drive hub 36 to be retracted into therotor 42 until an abutment shoulder inside the brake release member 56engages the latch unit 66 to limit the descent of the drive hub 36 andbrake release member 56. The motor is then stalled until the ligament 70is released and thus the latch element 68 is disengaged from the splines74.

For further illustration, the operation of the drive hub mechanism isillustrated in FIGS. 8A and 8B. In the situation shown in FIG. 8A, thehub 36 has been raised, but the latch element 68 has not yet beenreleased. In FIG. 8B, the hub 36 has been retracted, and the latchelement 68 has been released. Referring to FIG. 8A, it can be seen that,once the hub has been raised, drive dogs 74 are engagable with the driveteeth of the supply reel 22 in the cartridge housing 10, and a centralprojection 76 on the hub is engagable with the locking button (notshown) of the cartridge 10. As also shown in FIG. 8A, the latchingelement 68 of the latch unit 66 may be arranged so that it is biasedupwardly upon tensioning of the ligament 70 so that it can maintainengagement with the splines 74 of the brake release member 56 despitethe upward movement of the drive hub 36 and the brake release member 56.

3.3 Head Indexing

Referring now to FIG. 9, there is illustrated schematically anarrangement for indexing a tape head across the width of a magnetictape, and also for adjusting the azimuth angle of the head.

The head is mounted on a head mounting plate 80, which in turn ismounted on two parallel screws 82, 84. Gears 86, 88 are mounted on thescrews and are driven by a common pinion 90 on a motor 92, such as astepper motor or a DC motor and encoder. The gear 88 is directlyattached to the screw 84. However, a backlash device 94 is providedbetween the gear 86 and its corresponding screw 82 so that the gear 86can rotate through an angle of, for example, 30 degrees, without causingany rotation of the screw 82. Also mounted on the plate 80 is a pivotedstop lever 96, one end of which can engage a reference surface 98, andthe other end of which can engage a stop pin 100 provided on the gear86.

The operation of the mechanism will now be described with reference toFIGS. 10A to 10E. During initialisation of the tape drive machine, themotor is rotated to move the head plate 80 down the screws 82, 84 untilthe stop lever 96 engages the reference surface 98 and causes the otherend of the stop lever 96 to swing into the path of the stop pin 100 andthus stall the motor. This situation is shown in FIG. 10A. During thisoperation, the backlash in the backlash device 94 will be taken up.Friction between the drive screw 82 and head mounting plate 80 ensuresthat motor 92 removes all backlash before the drive screw 82 moves, andprevents displacement of the head by vibrations.

Taking the example of a simple case, in which the same azimuth angle isused for movement of the tape in either direction, the number A ofdegrees of rotation of the stepper motor required to move the headmounting plate 80 from the initialisation position to the desiredazimuth angle is remembered by a controller for the motor. If, from theposition shown in FIG. 10A, the motor is caused to rotate by A degrees,then the screw 84 will rotate to raise the right hand side of the headplate 80. However, the number B of degrees of rotation of the motornecessary to take up all of the backlash in the backlash device ischosen to be greater than the number of degrees A, and therefore thescrew 82 will not rotate. Therefore, from the initialisation positionshown in FIG. 10A, rotating the motor by A degrees will move the headplate 80 so that the head is aligned with the first track on the tapeand the azimuth angle is correct.

The controller for the motor is also programmed to remember the number Iof degrees of rotation to move the head from one track to the nexttrack. From the position in which the head is correctly aligned on thefirst track, if it is desired to move the head to the third track,firstly the motor is rotated B-A steps to take up the remainder of thebacklash in the backlash device 94, only the screw 84 being rotatedduring this operation. Rotation of the motor is continued for a further2×I degrees, during which time both screws 82, 84 rotate, and the screw82 is brought to the desired position. This situation is shown in FIG.10B. Then, the motor is rotated in the opposite direction by B-Adegrees, causing only screw 84 to rotate due to the backlash device 94,and bringing the head plate to the desired azimuth angle as shown inFIG. 10C.

If it is then desired to move the head in the opposite direction, forexample by one track from track three to track two, firstly the motor isrotated by B degrees to take up the backlash in the backlash device 94and to cause only screw 84 to rotate. Rotation of the motor by 1×Idegrees is then carried out to cause both screws 82, 84 to rotate and tobring screw 82 to the desired position, as shown in FIG. 10D. The motoris then rotated in the opposite direction by A degrees to cause onlyscrew 84 to rotate and to bring the head plate 80 to the desired azimuthangle, as shown in FIG. 10E.

It will be appreciated that a more sophisicated control arrangement canbe utilised so that differing azimuth angles can be set, depending onthe direction of movement of the tape. Furthermore, the azimuth angle ofthe head may be easily adjusted by storing a different value of A to beused by the controller for the stepper motor 92. Furthermore, othermethods to establish datums can be used.

Referring back to FIG. 9, the centre of the head with respect to themounting plate 80 is denoted by reference numeral 102, part way betweenthe screws 82, 84. Therefore, with varying azimuth angles, the positionof the head across the width of the tape will also be altered slightly.This can be compensated for by introducing an offset into the positionof the screw 82 between the initialisation position, shown in FIG. 10Aand the position of the screw 82 used for reading the first track, andby varying this offset in dependence upon the set azimuth angle of thehead. Alternatively, the head may be mounted on the mounting plate 80 sothat it is aligned with the screw 82.

It should be noted that the variations in azimuth angle shown in FIGS.10A to 10E have been exaggerated for the purposes of clarity.

3.4 Tape Drive Motor

Referring now to FIGS. 8A, 8B and 11 to 14, there follows a descriptionof a motor for use in the tape drive machine. The rotor 42 of the motorcomprises the cylindrical member 44 described above, and an annularflange 104 extending radially outwardly from the cylindrical member 44at the upper end thereof. The inner raceway of a ball bearing 106encircles the cylindrical member 44.

The stator 108 of the motor comprises a back iron 110 formed from astrip wound in a spiral. Eighteen winding coils 112 are disposed on theback iron 110 in a manner described below, and the assembly of thewindings and back iron is potted in a reinforced thermosetting plasticsresin to form an annular stator. A rebated bearing mounting ring 114 isprovided internally of the stator assembly, and the other raceway of thesingle ball bearing 106 is fitted into the rebate of the ring 114.

A plurality of magnets 116 are secured to the underside of the flange104 of the rotor to provide twelve alternating north and south polesconfronting the arrangement of winding coils 112. The windings arecontrolled by a brushless DC motor controller integrated circuit toproduce a rotating magnetic field, and accordingly the rotor 42 rotatessynchronously with the magnetic field.

It will be noted from FIG. 11 that the motor has a small axial height,by comparison to its diameter, and typically the height of the motorwould be 12 mm for the application in the tape drive machine describedabove. The design of the low height of the motor is facilitated by theuse of a single bearing for mounting the rotor to the stator.Furthermore, an important advantage of the motor is that there is anaxial component to the magnetic field between the rotor and the stator,and this axial component tends to take up any play in the bearing 106,without the necessity of any other means such as a spring or shims.

The diameter of the bearing assembly is a substantial proportion, suchas at least one quarter and more preferably at least about one half ofthe diametrical size of the motor. In one example, the balls of thebearing follow a path of diameter 52 mm and the stator assembly has anoutside diameter of 98 mm. Furthermore, the balls of the bearingassembly are preferably of small diameter relative to the diameter ofthe path which they follow, for example in the ratio of 1:14.8. In theexample where the balls follow a path of diameter 52 mm, the balls areeach of diameter 3.5 mm. By making the bearing of large diameter withballs of small diameter, the amount of tilt of the rotor due to play inthe bearing is small.

3.5 Stator Construction

Referring specifically to FIGS. 12 to 15, the arrangement of the windingcoils 112 is illustrated. Eighteen such coils are provided and they areinterconnected in a three-phase, twelve-pole arrangement. Inconstruction of the coil assembly, each coil is initially substantiallyplanar. The coils are laid on an annular former in two tiers in thearrangement shown in FIG. 12, and a further annular former is placed ontop of the upper tier of coils. The width of the annular former isslightly less than the distance between the two circumferential portionsof each coil. The two formers are then pressed together in a press inorder to deform the coils so that each generally radial portion x ofeach coil is forced into the space between the generally circumferentialportions of the adjacent coil, and thus the sections as shown in FIGS.14 and 15 are obtained. Each coil is covered with a heat-curablelacquer, and after the pressing operation the coil assembly is heated inorder to cure the lacquer coating and thus bond the coils together in arigid ring. This manufacturing process therefore provides a compact andstrong winding assembly.

The stator assembly may be formed from three or more tiers pressedtogether, rather than two tiers.

3.6 Detection of Tape Edge

Referring to FIGS. 17 to 19, an arrangement is illustrated for detectingone of the edges of the magnetic tape. A laser diode is disposed to oneside of one edge 152 of the tape 154. The diode 150 emits a beam oflight which, at the diode, is very narrow in one direction, typically1.5 microns, and this narrow direction is arranged to correspond withthe width direction of the tape. The beam of light diverges from thediode 150, and the diode is arranged so that the tape 154 partially cutsthe beam of light. The light beam is directed to a photo sensor array156. The distance x between the diode 150 and the tape 154 is chosen tobe substantially less than the distance y between the tape 154 and thephoto sensor array 156. In one example, the distance x is 1 mm, and thedistance y is 30 mm.

Referring specifically to FIG. 18, the photo sensor array 156 comprisesfour photo sensitive elements 158, arranged in a two-by-two array, withthe diagonals parallel to and perpendicular to the edge of the shadow160 of the tape 154 cast by the diode 150. An arithmetic circuit 162serves to sum the outputs of the sensor elements 1, 3, to sum theoutputs of the elements 2, 4 and to provide an output dependent upon thedifference between the two sums. The output therefore provides a measureof the transverse position of the tape and has a nominal zero value whenthe shadow of the edge 152 of the tape bisects the sensor elements 2, 4.Four sensor elements are used so that any offset in the output of eachsensor element, which is likely to be the same for all four sensorelements, is self cancelling. The output from the arithmetic circuit 162may be used in initially setting the position of the head of the tapedrive. However, the output may also be dynamically used when indexingthe head in the arrangement described above to compensate for anyvariations in the transverse position of the tape. Furthermore, in onearrangement which provides for movement of the head across the tapecompletely independently of azimuth adjustment of the head, the tapeedge may be continuously detected and the head may be moved at any timeto compensate for variations in the transverse position of the tape.

An alternative photo sensor 156 is illustrated in FIG. 19. In this case,only two sensor elements are used. Sensor element A1 is in the form of adisc, and sensor element A2 is in the form of a ring concentric with theelement A1 and of the same area. A simpler arithmetic circuit can thenbe utilised which merely provides an output dependent upon thedifference between the outputs of the sensor elements A1, A2.

In the above arrangement, by virtue of the large ratio of the distance yto the distance x, movement of the edge of the tape relative to thediode 150 and the photo sensor 156 produces a greatly amplified movementof the edge of the shadow 160 cast by the tape 154. Accordingly, thearrangement can be used to determine the position of the edge of thetape to very fine tolerances.

3.7 Detection of Beginning and End of Tape

Referring to FIG. 16, there is shown a manner of controlling the motor.The windings of the motor are arranged as three phases 118, 120, 122 ina star configuration. Each winding is connected to an output of anelectronic commutator circuit 124. A generator 126 supplies a 50 kHzsignal which is modulated by a pulse width modulator 128, and the pulsewidth modulated signal is supplied to the electronic commutator 124 forswitching between the three phase outputs of the commutator 124.Hall-effect sensors 130 responsive to rotation of the rotor of the motorsupply synchronising signals to a controller 132, and the controller 132provides synchronising signals to the commutator 124 so that the pulsewidth modulated signal is switched to the respective phases of thewindings at the appropriate times. A speed setting device 134 provides asignal to the controller 132, and the controller 132 provides a signalto the pulse width modulator 128 dependent upon the set speed and theactual speed derivable from the output of a tachometer B which can befitted either to the motor or placed in the tape path to measure thespeed, so that the pulse width is varied to regulate the speed of themotor.

It is necessary in a tape drive machine to be able to detect that thetake-up reel is nearly empty, so that the motors can be halted beforethe end of the tape is reached, in order to prevent undue straining ofthe tape, or the leader block being forced out of take up reel and pastthe head assembly.

Referring to FIG. 16, the tachometer 133 produces a series of pulses,for example 360 pulses for each revolution of the tachometer, which arecounted by the controller 132. The controller 132 also responds to anoutput from one of the Hall-effect sensors 130 for the take-up reel toreset the count once per revolution of the take-up reel. It will benoted that the radius R of the body of tape on the take-up reel can bedetermined by the value n of the count immediately before the count isreset by the equation R=n.r/N, where r is the radius of the tachometer133 and N is the number of pulses produced per revolution of thetachometer 133. During fast or slow reverse winding, the controller 132is operable repeatedly to determine whether the value n is less than apredetermined value indicating that the radius of the body of tape onthe take-up reel is only slightly greater than the radius of the take-upreel, and upon such a determination is operable to stop the windingprocess. Thus, winding is stopped just before the beginning of tape isreached.

In a modification of the above process, the controller is also operablerepeatedly to determine whether the value n is greater than a furtherpredetermined value indicating that the radius of the body of tape onthe take-up reel has reached a maximum permissible value, and to stop aforward winding process upon such a determination. The maximumpermissible radius is chosen to be somewhat less than the radius whichwould be produced if all of the tape were wound onto the take-up reel.

Since the value of the maximum diameter of the body of tape on thetake-up reel depends on the length and thickness of the tape, which mayvary from one tape cartridge to another, in an alternative preferredmodification the controller determines the end of tape using one of theHall-effect sensors of the supply reel motor and can therefore determinewhen the radius of the body of tape remaining on the supply reel hasdecreased to value only slightly larger than the radius of the supplyreel.

3.8 Last Turn Sensor

Referring to FIG. 20, a printed circuit board 188 for carryingelectronic components of the machine is provided beneath a take-up motor190 which drives a take-up reel 170. An infra-red source 194 is mountedat one position on the printed circuit board 188, and an infra-reddetector 192 is mounted at another position. The infra-red source 194projects a beam upwardly through a passageway 204 in the motor and apassageway 202 in the boss 172 to a reflective surface 200. The beam isreflected by the surface 200 into a part-chordal passageway 198 in theboss 172 of the take-up reel 170, and passes to a mirror 196 provided ona mounting plate 186, which directs the beam downwardly through onto theinfra-red detector 192. The beam will only follow this path when thetake-up hub 170 is in a position in which the passageway 198 is alignedwith the mirror 196 and when the passageway 202 is in register with thepassageway 204 and when there is slightly less than one turn of tape onthe take-up reel 170. If there is more tape than this, then it will beappreciated that the exit from the passageway 198 is covered by thetape.

It will be appreciated that the above arrangement enables the electroniccomponents, that is the infra-red source and infra-red detector to bemounted directly on a main circuit board 188 of the tape drive machine.

We claim:
 1. A tape drive for a tape cartridge (10) of the type having agenerally flat cartridge housing with top and bottom faces (12, 14) anda peripheral edge (16) extending between the top and bottom faces and adrive hub receiving member (22) accessible through the bottom face ofthe housing, the tape drive comprising:a drive housing (30); means tohold such a cartridge in an operating position in the drive housing; adrive hub (36) arranged to engage the drive hub receiving member of sucha cartridge in the operating position; an electric motor (34) arrangedto drive the hub; and means (46, 48) to retract the drive hub out ofengagement with the hub receiving member to permit the cartridge to bewithdrawn from the operating position substantially by sliding movementin an edgewise direction of the cartridge; characterized in that: themotor has a main body (34) disposed in the drive housing directlybeneath the cartridge when in the operating position, the main bodyhaving a cavity; and the drive hub is retractable from a position (FIGS.3, 8A) projecting from the motor body into engagement with the hubreceiving member of the cartridge to a position (FIGS. 4, 8B) retractedinto the motor body that said drive hub is substantially, entirelycontained within said cavity whereby the drive hub does not projectsubstantially from the motor body and is clear of the cartridge.
 2. Atape drive as claimed in claim 1, wherein the housing (30) is adapted toreceive a cartridge having nominal dimensions of 127 mm (5") long, 102mm (4") wide and 25 mm (1") high.
 3. A tape drive as claimed in claim 2,wherein the housing is adapted to receive a cartridge according tospecification IBM GS 32-0048-0, ECMA 120, ANSI×3B5-87-037, or asubstantially equivalent specification.
 4. A tape drive as claimed inclaim 1, wherein the drive has overall dimensions of substantially 83 mm(3.25 ") high, 146 mm (5.75") wide and not greater than 203 mm (8")long.
 5. A mechanism as claimed in claim 1, wherein the means to retractthe drive hub comprises at least one projection on one of the rotor andthe hub engaging in a complementary groove in the other of the rotor andthe hub.
 6. A mechanism as claimed in claim 1, wherein the means toretract the drive hub comprises at least one pair of grooves in the huband rotor respectively, and a rolling transmission element engaging bothgrooves of the pair.
 7. A drive mechanism for a tape drive machine,comprising a motor (34) having a rotor (42), a tape reel drive hub (36)arranged to be driven by the motor and for engaging and driving a tapereel in the tape drive machine, means (46, 48) to cause the hub to movein axial directions between first and second opposite axial positions(FIG. 8A, FIG. 8B), and means (52) selectable to lock the hub in atleast the first axial position, characterized in that the rotor isannular, the hub is mounted within the rotor, the movement causing meansis operable to cause the movement between the first and second oppositeaxial positions in response to relative rotation of the hub and rotor infirst and second opposite directions, and the locking means is operableto permit rotary drive to be transferred from the rotor to the hub whenthe hub is in the first axial position.
 8. A mechanism as claimed inclaim 7, wherein the hub projects from the rotor in the first position(FIG. 8A) and is retracted into the rotor in the second position (FIG.8B).
 9. A mechanism as claimed in claim 8 wherein the means to cause thehub to move axially comprises a screw thread (46) or the like actingbetween the hub and the rotor.
 10. A mechanism as claimed in claim 8wherein the hub is prevented from moving past the first axial positionfrom the second axial position with respect to the rotor, and whereinthe locking means comprises a brake (52) operable to prevent relativerotation between the hub and the rotor in the direction which wouldcause the hub to move from the first to the second axial position withrespect to the rotor.
 11. A mechanism as claimed in claim 7 wherein themeans to cause the hub to move axially comprises a screw thread (46) orthe like acting between the hub and the rotor.
 12. A mechanism asclaimed in claim 11, wherein the means for causing the hub to moveaxially comprises at least one projection (48) on one of the rotor andthe hub engaging in a complementary groove (46) in the other of therotor and the hub.
 13. A mechanism as claimed in claim 12 wherein thehub is prevented from moving past the first axial position from thesecond axial position with respect to the rotor, and wherein the lockingmeans comprises a brake (52) operable to prevent relative rotationbetween the hub and the rotor in the direction which would cause the hubto move from the first to the second axial position with respect to therotor.
 14. A mechanism as claimed in claim 11, wherein the means tocause the hub to move axially comprises at least one pair of grooves inthe hub and rotor respectively, and a rolling transmission elementengaging both grooves of the pair.
 15. A mechanism as claimed in claim14, wherein the hub is prevented from moving past the second axialposition and the first axial position with respect to the rotor, andwherein the locking means comprises a brake operable to prevent relativerotation between the hub and the rotor in the direction which wouldcause the hub to move from the first to the second axial position withrespect to the rotor.
 16. A mechanism as claimed in claim 14 wherein thehub is prevented from moving past the first axial position from thesecond axial position with respect to the rotor, and wherein the lockingmeans comprises a brake (52) operable to prevent relative rotationbetween the hub and the rotor in the direction which would cause the hubto move from the first to the second axial position with respect to therotor.
 17. A mechanism as claimed in claim 11 wherein the hub isprevented from moving past the first axial position from the secondaxial position with respect to the rotor, and wherein the locking meanscomprises a brake (52) operable to prevent relative rotation between thehub and the rotor in the direction which would cause the hub to movefrom the first to the second axial position with respect to the rotor.18. A mechanism as claimed in claim 7 wherein the hub is prevented frommoving past the first axial position from the second axial position withrespect to the rotor, and wherein the locking means comprises a brake(52) operable to prevent relative rotation between the hub and the rotorin the direction which would cause the hub to move from the first to thesecond axial position with respect to the rotor.
 19. A tape drive for atape cartridge (10) of the type having a generally flat cartridgehousing with top and bottom faces (12, 14) and a peripheral edge (16)extending between the top and bottom faces and a drive hub receivingmember (22) accessible through the bottom face of the housing, the tapedrive comprising:a drive housing; means to hold such a cartridge in anoperating position in the drive housing; and a drive mechanism mountedin the drive housing, the device mechanism comprising a motor (34)having a motor body (34), an annular rotor (42), a tape reel drive hub(36) mounted within the rotor and arranged to be driven by the motor,means (46, 48) to cause the hub to move in opposite axial directionsbetween a first axial position projecting from the motor body forengagement with the drive hub receiving member of the cartridge and asecond axial position in which the drive hub does not project from themotor body, and means (52) selectable to the lock the hub in at leastthe first axial position, the movement causing means being operable tocause the movement in the opposite axial directions in response torelative rotation of the hub and rotor in first and second oppositedirections of rotation, and the locking means being operable to permitrotary drive to be transferred from the rotor to the hub when the hub isin the first axial position.